In motor-driven systems and devices with hydraulic systems, for example, in loader-like and excavator-like construction machinery, for reasons of costs, typically the output of the diesel engine is used to drive the hydraulic pump without reserves. Likewise, for reasons of costs, in many cases the hydraulic pump is not designed such that with a simultaneously maximum volumetric flow demand of all consumers, sufficient supply of all consumers would be ensured.
In working operation, this limitation leads to the diesel engine being operated at its output limit and the pump flow rate in parallel operation of hydraulic consumers not being sufficient for the desired maximum working speeds. For safety functions, priority valves must be used to supply the preferred consumers first before delivery to other consumers is released. All other consumers must share the remaining flow.
For such construction machinery, the prior art t supplies the consumers by directional control valves with compensators connected upstream. The valve spools of the directional control valves determine the size of the opening of the metering orifices for supply of the consumers. Viewed from the pump, a series of variously high resistances is presented by the operating principle of the upstream compensators copying the pressure of the external loads to upstream from the metering orifices and still increasing it by the amount of force of their control springs. When the flow rate of the pump is insufficient, the pump pressure collapses, and the working medium flows over the path of least resistance. The consumer with the highest load can thus be shut down. Its “saved” volumetric flow is thus available to all other consumers.
For the machine operator, this system behavior is not acceptable since, for typical machine control with a joystick, several functions are run at the same time. If one consumer inadvertently stops, the operator will experience difficulties with the controls.
The attempt to solve this problem by using valves with compensators connected downstream from the metering orifice does not lead to the desired success, even though downstream compensators do not copy the load pressure to upstream from the metering orifice. The highest load pressure in the system is copied to downstream from the metering orifice, as a result of which, when the pump pressure collapses, all resistances remain the same viewed from the pump. Disadvantageously in these systems, the amount upstream from the metering orifice must be separated. This separation is not easily possible. Another particular disadvantage is that the load signaling system of directional control valves with downstream compensators dictates a continuous discharge flow from the controlled volumetric flow of the consumer with the highest load. This operation constitutes an energy loss.